Manually metering of liquids can be difficult. This can be seen when one wants to get a certain amount of liquid (but not all of it) out of a tube. The tube collapses and there is no precise way of determining how much has been used or how much is left, short of using a measuring device such as a weigh scale. This is often not practical, particularly where work is being performed on a chargeable basis. Syringes and other injectors have been used for many applications, such as metering of epoxy resins and hardener. They typically lack precision.
Where one is injecting liquids into a pressurized system it may even be difficult simply to inject the entirety of the liquid.
As an example of circumstances where it is desired to meter liquids, injectors are often used in air conditioning and refrigeration systems. Such systems often leak which is undesirable. In air conditioning or refrigeration applications the system will not operate efficiently with reduced quantities of refrigerant. The missing refrigerant needs to be replaced. It is also undesirable as refrigerant can be environmentally damaging when released.
Leak detection can be performed by injecting a fluorescent dye into the system. In air conditioning and refrigeration applications dyes typically used for this purpose fluoresce in the ultraviolet and near ultraviolet region from approximately 360 to 420 nm; so, an ultraviolet light is shone on the system. Wherever leaks occur the dye will escape the system and fluoresce under the light. A pulsing ultraviolet light for this purpose is described in U.S. Pat. No. 5,804,822 issued Sep. 8, 1998 under title Fault Locating Device, System and Method. Many other ultraviolet lights are available.
A number of injectors have been developed for getting liquids into air conditioning and refrigeration systems. Some injectors may also be used to inject other liquids, for example, refrigerant, lubricant and/or other additives into the air conditioning system.
The assignee of the instant application is the owner of U.S. Pat. No. 6,263,778 issued Jul. 24, 2001 under title Precision Liquid Injection System. The system has a spindle with a central bore into which a piston is inserted. The piston and spindle define a chamber that carries the liquid to be injected. A driver sleeve has interior threads that match those on the outside of the spindle. A piston rod is placed inside the driver sleeve. Rotation of the driver sleeve causes the piston rod to drive the piston into the chamber. The liquid escapes through an opening at the end of the spindle and is injected in to the system.
Although the system works well, improvements are desirable as with any product.
It is an object of the invention to provide such improvements, to address other problems associated liquid injectors, or to provide alternative devices.